Download Design and Construction vs. Weather

eather conditions affect
the design, construction,
and performance of
buildings. The intent of
this article, while pre­
senting the cause and
effect of weather, is to improve the under­
standing of how varying
weather conditions can
affect construction pro­
jects. Armed with this
information, building pro­
fessionals can take mea­
sures to eliminate (or at
least reduce) the impact of
weather.
Meteorology is one of
my hobbies, and I have a
special interest in how
weather affects building
design and construction. I
have read many old
weather sayings that have
been repeated over the
years. Some are based on
scientific principles and
are frequently dependable,
but that is beyond the
scope of this article. Some of these sayings
include:
• Every wind has its weather!
• Rain before seven, gone by eleven.
• Dew in the night, next day will be
bright.
W
20 • INTERFACE
• When in February you hear thunder,
ten days later, you’ll be snowed
under.
• When wooly fleeces show the heav­
enly way, no rain will disturb the
summer day.
statistics for specific cities or states are
available from the National Weather Service
and from various private climatic agencies
such as AccuWeather. This data can be
incorporated into the building during
design and can influence construction
materials selected and the construction
means and methods used.
THE CAUSE
Weather is simply a
reaction to changes in
atmospheric
pressure.
These changes alter air
movement, temperature,
and
humidity.
Some
changes are dramatic and
produce violent storms.
Other changes are subtle
and have little effect on
weather. Meteorologists can
predict these changes with
reasonable
short-term
accuracy. What is done with
these predictions directly
affects comfort, project
design, and construction
procedures.
The various geographic regions
throughout the world have prevailing
weather patterns that are typical for a spe­
cific region. Climate maps that include wind
speed, rainfall, and snow accumulations
are published in model code books. Climatic
THE EFFECTS
Weather conditions can affect many
aspects of the construction project from site
work to worker comfort. For the purpose of
this discussion, weather conditions are
FEBRUARY 2005
divided into hot and dry, cold, wet, thunderstorms, and windy. The
most common effects are briefly mentioned for each condition.
Hot and Dry Conditions:
It may be surprising to consider hot and dry weather as a prob­
lem. However, a lack of moisture can have dramatic effects on a
project, especially on outside activities. Just what is affected dur­
ing these conditions?
Site: Dust is associated with with hot and dry weather. One of
the easiest ways to be tagged a bad neighbor is to allow large clouds
of dust to settle on nearby property. Tanker trucks are often used
to spread a water mist over designated areas to reduce dust. Dust
also generates dirt that must be removed from interior surfaces on
a regular basis during construction.
Concrete: Dry weather can cause the water in concrete and
masonry to evaporate too fast. This rapid evaporation produces
concrete with a lower compressive strength and a finished concrete
that tends to curl upward and to spall.
Masonry Mortar: Dry weather causes rapid evaporation of
moisture, which causes the mortar to begin setting prematurely.
When mortar begins to set prematurely, there may not be sufficient
moisture to ensure the brick absorbs the mortar paste properly.
This reduces the bond strength between the mortar and the brick,
which is a major cause of masonry leaks.
Brick: Unless properly wetted prior to laying, bricks become
excessively dry and when laid, they absorb the water from the mor­
tar so fast that the mortar paste that creates the bond between the
brick units is not absorbed. When this occurs, a poor bond is
formed, and can cause masonry leaks at the joints.
Paint: Weather can affect both application and performance of
paint. During application, when ambient temperature or surface
temperature of the substrate is too high or the relative humidity is
low, reducers (solvents) in paint evaporate too fast. This rapid evap­
oration prevents the paint from curing properly, possibly causing
delamination, wrinkles, blisters, peeling, and cracking. Most paint
containers state the ambient and substrate temperature range.
Some paint manufacturers include a recommended relative humid­
ity range. Ultraviolet (UV) exposure is the worst enemy of paint per­
formance. Eventually, all paint will succumb to UV, ultimately
prompting fading, chalking, and embrittlement. However, some
paints, such as high performance polyurethane and 100 percent
acrylic, are formulated to be more resistant to UV exposure.
Seals and Sealants: All weather, especially freeze-thaw cycles
and UV exposure, will reduce the resiliency of seals and sealants,
resulting in a loss of elasticity. Loss of elasticity causes embrittle­
ment. Replacing failed sealants can be an expensive endeavor
because new product installed directly over an old sealant usually
results in premature failure. To prevent premature failure, the
failed material must be removed, the joint thoroughly cleaned, and
new and proper sealant installed. Using high quality elastomeric
sealants such as silicone and polyurethane usually prolongs the
integrity of a sealed joint. Manufacturers often have details for joint
design that provide for temporary protection from moisture intru­
sion if the sealant fails. However, these joint designs are not a sub­
stitute for a proper joint sealant.
Equipment: Filters on vehicles, machinery, and equipment,
both inside and outside, are exposed to dusty conditions. These fil­
ters should be checked and changed regularly to prevent premature
breakdowns. Dust can also find its way into working parts and
FEBRUARY 2005
INTERFACE
• 21
Painting: Cold temperatures
can cause the carriers (water in
water-based paints and solvents in
solvent-based paints) to freeze or
thicken and retard the curing
process. Condensation, which is
moisture that forms on surfaces
when air temperature falls below
the dew point, usually leads to premature paint failure. Dew point is
directly related to temperature and
relative humidity and is often asso­
ciated with cooling temperatures.
When condensation forms with
surface temperatures above freez­
ing, the resulting moisture is called
dew. Conversely, when condensa­
tion forms with surface temperatures below freezing, the resulting
moisture is called frost.
Equipment: Water-cooled en­
gines must be winterized and protected from cold temperatures.
Like people, equipment can act a
little sluggish when it is cold. Cold
lubricants are not effective, and
operating equipment with inade­
quate lubrication can cause accel­
erated wear of moving parts. Be
patient; give equipment sufficient
time to warm up before operating
it.
Workers: Workers must wear
extra clothing that is often heavy
and bulky. When it is cold, everyone looks like the Michelin Man®.
Bulky clothing can restrict movement and increase the risk of acci­
dents. Also, muscles and joints are
not as flexible and are more sus­
ceptible to injury when cold. Both
dew and frost on smooth surfaces,
such as single-ply roofs, metal
roofs, smooth concrete, and struc­
tural steel, can cause falls.
Drinking water must be protected
from freezing.
cause accelerated wear. Equipment should be cleaned and
lubricated regularly.
Thermal Movement: Based
on their respective thermal coeffi­
cients of expansion, some materi­
als will move significantly more
than others when exposed to temperature variations. For example,
aluminum has a higher thermal
coefficient of expansion than
stainless steel and will experience
more movement. However, con­
trary to common assumption,
thickness does not affect the
amount of movement. Thus,
0.032-inch thick aluminum sheet
will not move any more than
0.125-inch thick extruded alu­
minum. However, when thick and
thin pieces of aluminum are fastened to a substrate, the thick
piece of aluminum, because of its
mass, will exert more pressure on
the fasteners than the thin piece
of aluminum. When a design does
not allow for thermal movement,
joints or seams can open, fasten­
ers can fail, and components can
distort or break. Both expansion
from heat and contraction from
cooling should be considered dur­
ing design and construction.
Workers: Physical activity
associated with construction
work will cause a considerable
loss of body fluid. Since it is
imperative that this body fluid
loss be replenished, fresh water
should be readily available to
workers to prevent dehydration,
especially to those outside.
Drowsiness, disorientation, dizzi­
ness, and fatigue are common
symptoms of dehydration and can
result in lost-time accidents or
sickness.
Cold Conditions:
Concrete and Masonry: Cold
weather can cause ice crystals to form and
retain moisture. Cool temperatures can also
slow the curing, which may affect concrete
strength, promote spalling, and can ruin
the finish. Cold weather procedures recom­
mended by the American Concrete Institute
(ACI) for concrete work and Brick Institute
of America (BIA) for masonry should be fol­
lowed.
Site Freezes: When the site freezes,
22 • INTERFACE
water is retained in the earth so that sur­
face drying is slowed, resulting in prolonged
muddy conditions.
Foundations: In cold climates, founda­
tion bases must be set below the frost line
to prevent heaving. The colder the climate,
the deeper the frost line, and consequently,
the deeper the foundation. If the foundation
is above the frost line, freeze-thaw cycles
can cause excessive structural movement.
Wet Conditions:
Yes, wet weather is the opposite
of dry weather and unlike dry weather, it
can cause more problems, big delays, and
increased costs. Wet weather is frequently
the reason contactors use to request
increased contract time or money.
Site Work: Rains can turn a construc­
tion site into a gigantic mud hole that would
make a “4-wheeler” drool with envy. Mud
will hinder access to the site by all building
trades and will prevent or slow general
FEBRUARY 2005
earthwork (grading, trenching, and backfill­
ing activities), paving, and foundation work.
Both foot and vehicle traffic can be restrict­
ed, and compacted gravel or rock is often
used in roadways to establish a firm base.
The site should be properly graded to
ensure positive drainage away from the
structure and to prevent water collection
points.
Groundwater: A high water table or
excessive rain can increase groundwater.
Regardless, dewatering provisions for exca­
vation and trenching must be used to keep
the site and excavations dry enough to allow
steady progress. Furthermore, including
permanent waterproof­
ing for below-grade
spaces in the building
design will compensate
for high water table and
groundwater
condi­
tions.
Brick: Brick is a
reservoir for moisture,
and capillary action
causes it to suck up
moisture like a dry
sponge. As damp brick
heats up from the sun,
the warmth causes the
moisture to move to­
ward the cooler interior.
Unless the building is
designed and con­
structed with an interi­
or rain screen and
through-wall flashing,
the moisture will con­
tinue to migrate inward and condense on
the cooler interior wall. In additions, poorly
constructed or tooled masonry joints are
openings for moisture intrusion. When
brick emerges from the kiln, it is the small­
est that it will ever be. But it expands as it
absorbs moisture. The expanding brick can
break adjacent brick and open mortar
joints. Properly designed and constructed
expansion joints will compensate for this
movement.
Fibrous and Porous Products: Fibrous
and porous materials that include wood,
fibrous insulation, drywall, carpeting, and
masonry are examples of materials that
absorb and hold moisture. Moisture in or
on these materials is a prescription for the
dreaded ”M” word – mold. To prevent dis­
tortion and damaged finishes, these items
should be kept dry and protected before,
during, and after construction.
Paint: When relative humidity exceeds
the manufacturer’s recommended limits, or
when fog or mist are present, paint will not
cure in the normal time. This can cause
poor adhesion, discoloration, and can give
additional time for dirt to settle on the
uncured and tacky surface.
Building: Building performance can be
significantly improved by draining every­
thing from the roof to the foundation.
Moisture is an intruder that will penetrate
the building shell of the best defended
structure. However, once moisture breaches
the building shell, drainage provisions can
be used to capture it and direct it to the
exterior.
THUNDERSTORMS
Thunderstorms are simply rain with an
attitude, plus light and sound for special
effects. Usually, the darkening sky and tow­
ering dark clouds give warning of an
approaching thunderstorm. Other times,
they occur suddenly. They are particularly
dangerous to workers and to tall structures,
especially those in the
open. Workers should
seek inside protection
on the ground floor or
basement away from
steel, windows, and
doors.
Straight-line
winds (sometimes ap­
proaching hurricane
velocity) that usually
accompany thunder­
storms can wreak
havoc on construction
sites.
Construction
crews should ensure
that materials are
properly secured and
protected, construction
in process is properly
braced, trash and
debris are in containers
that are properly
secured, and personal
protection measures are taken. Also, build­
ings in areas with frequent thunderstorms
should be designed with lightning protec­
tion.
Thunderstorms often include hail and
wind. The National Weather Service consid­
ers severe hail to be 3/4-inch diameter
(dime size). However, smaller size hail can
break windows and severely damage
exposed materials such as sheet metal and
roofs – especially shingles and single-ply
roofs. It will dent and deform sheet metal
and strip thin paint from substrates. Where
severe thunderstorms are common, consid­
er roof systems that are resistant to hail.
Occasionally, a thunderstorm produces
the T-Rex of storms – the tornado. Usually
short-lived, these guys suck up anything
not properly anchored and spit out debris
all over the place. Metal buildings seem to
be their preferred diet. Sometimes it seems
that tornadoes will hop over masonry or
concrete structures to get to a metal build­
ing. Since tornado shelters are under­
ground, what does that suggest about
designing and constructing in areas that
have frequent tornadoes?
Hurricanes are storms with a really,
really bad attitude, and they usually spawn
thunderstorms that can produce tornadoes.
However, hurricanes typically occur in
southern Atlantic and gulf coast regions of
the United States. During design and con­
struction, special consideration and atten­
tion must be given to the model building
code requirements for these areas.
WIND
In most instances, wind can dramatical­
ly multiply the effects of the previously dis­
cussed elements. Wind increases drying by
accelerating the removal of moisture (notice
how your lips chap in the wind). It reduces
cooling time by accelerating the removal of
heat (we blow on hot soup to cool it quick­
er). Wind drives moisture into the structure
by increasing the pressure on the film of
moisture on the surface of the structure (we
squirt openings with a high pressure hose
to test for leaks). It makes cold feel colder by
accelerating the evaporation of perspiration
(a jacket feels good on a windy day).
Wind damage can vary from removal of
a hard hat to rearranging staged materials
24 • INTERFACE
to blowing down an unsupported masonry
wall. Since tall, flat walls receive the full
impact of wind, it can move tall sky­
scrapers several feet off true
vertical. Walls that are
not structurally braced
and do not have provi­
sions for movement can tum­
ble down in a pile of rubble.
1. Roof: The geographic location
(coastal or inland area, open or
wooded area, urban or rural area,
etc.) of a structure, or the building
shape and building height can influ­
ence the wind uplift pressure on a
roof. High winds can produce suffi­
cient wind uplift forces to cause
severe damage or a complete blow
off. This puts a different meaning on
the expression, “raise the roof.”
Building design should consider
building location, shape, and height,
and the projected wind speed. For
example, a flat roof with loose stone
in a southern coastal location is not
a good idea.
2. Doors and Windows: Air and mois­
ture infiltration are directly propor­
tional to pressures produced by the
wind speed. The anticipated wind
speed and the height of doors and
windows must be calculated into
their design and installation. In arid
climates, fine dirt can easily filter
through unnoticeable cracks in
doors and windows and leave a
small furrow of dirt along the crack.
SUMMARY
Weather is always here. It is always
around us. As the old saying goes, “Every­
one talks about the weather, but no one
does anything about it.” True, weather can­
not be controlled. But, building profession­
als can prepare for it and adjust to resulting
conditions. Proper preparation, adjustment,
and reaction to local weather will influence
the success of a construction project and
the completed building.
Weather extremes can test building per­
formance. Building performance can be
improved with insulation, corrosiveresistant metals, decay-resistant wood, UVresistant paint and sealant, selective roof
systems, drainage planes, permanent flash­
ing, positive drainage everywhere, and high
performance windows and doors with high
performance glass.
Even landscaping can affect building
performance. Deciduous trees (trees that
shed leaves in fall) can provide cooling dur­
ing summer when the leaves block the sun.
In the winter, when the leaves are gone, the
sun shines through the bare trees to pro­
vide warmth.
Roofs are usually the highest part of a
building, and they stick out like a sore
thumb. Consequently, roofs probably get
more abuse from UV, moisture in both solid
and liquid states, and the wind than any
other part of the building. Building profes­
sionals must provide the best roof system
for each application and then protect it dur­
ing construction. Additionally, roofing
crews, because of their work environment,
are most vulnerable to weather conditions
and should be provided with proper training
and protection relative to weather.
Joseph L. (“Cris”) Crissinger, CSI, CCS, CCCA
Joseph L. (“Cris”) Crissinger, CSI, CCS, CCCA, is a construc­
tion materials specifier with 22 years of experience. As a part­
ner with McMillan Smith and Partners, Architects, in Spartan­
burg, Greenville, and Charleston, SC, he evaluates new prod­
ucts and develops all written construction specifications for
the firm. His responsibilities also include facility assessment,
field investigations, and the coordination of internal training
programs. Crissinger is a Certified Construction Specifier, a
Certified Construction Contracts Administrator, and a mem­
ber of the Construction Specifications Institute, the Building Performance Committee of
ASTM, the Design and Construction Division of the American Society for Quality, and
serves in his community on the Board of Directors for the Spartanburg Boys’ Home and
the Camp Croft Restoration Advisory Board. McMillan Smith and Partners specializes in
the design of education, office, sports, healthcare, and church facilities and provides full
construction contract administration services.
FEBRUARY 2005